The present proposal seeks to provide detailed information concerning the nature of the stress proteins produced in ligament- derived fibroblasts and the ability of these proteins to protect cells from lethal challenges. The above will be accomplished through the fulfillment of 6 specific aims. (1) We will establish that a form of physical stress, heat shock, results in comparative differences in the ability for fibroblasts of diverse origin to survive. This will be determined by assaying the proliferative capacity of cells with a standard colony formation technique. (2) Verify that specific stress proteins are expressed in interosseous ligaments, (3) Substantiate that ubiquitin is a heat shock protein for interosseous ligaments by immunoprecipitation of free and protein conjugated ubiquitin in these cells, (4) Prove that the comparative differences among interosseous ligament-derived fibroblasts and fibroblasts of diverse origin to survive lethal challenges are correlative with the level of "stress-response" proteins, by statistical correlation of cell survival curves with the area of radioactivity of protein bands observed by autoradiography of Polyacrylamide gel separations of these proteins labelled with 35S-methionine, (5) Prove that interosseous ligament-derived fibroblast cells signals such as contact with collagens I, III, V and fibronectin, enhance the synthesis of collagen and also "turn-on" or amplify the cellular levels of heat shock proteins, (6) Finally, we will prove that when interosseous ligament-derived fibroblasts become quiescent and do not actively synthesize and secrete collagen that their susceptibility to physical stress is enhanced. Collectively these studies will help to explain the sensitivity of ligament-derived fibroblasts to physical insults and the prolonged periods necessary for repair of these structures.